Two critical factors in the flight of any aircraft or airplane are the weight and balance of that aircraft or airplane. Federal Aviation Administration regulations #FAR 23 & 25 of Title 14, Code of Federal Regulations, require an airplane manufacturer to determine and publish the maximum gross operating weight of an airplane. This is to insure that at take-off speed, the wings are generating sufficient lift to lift the weight of the airplane. A second but equally important factor to consider is whether the airplane is in balance (optimum location for the center of gravity) or within acceptable limits, as can be compensated for by trim adjustments.
Calculations to determine gross weight and center of gravity in terms of percent MAC (Mean Aerodynamic Chord) are well known and well documented. Reference may be made to U.S. Pat. No. 3,513,300 to Elfenbein. Prior art methods to determine gross weight and center of gravity are performed using measurements of some portions of the aircraft's payload and estimates of the remaining portions of the aircraft's payload. This information is input into ground computers which calculate gross weight and center of gravity. The calculations are relayed to the pilot in the aircraft before take-off, as illustrated by the following example:
A McDonald Douglas DC-10 Series 30 Airplane makes a daily nonstop flight from London to Dallas/Fort Worth Airport. On this transatlantic flight the airplane operates at a maximum gross weight of 560,000 lbs., capable of carrying a maximum 243,000 lbs. of fuel, with a useful payload of approximately 120,000 lbs. This useful payload is comprised of freight, in-flight service items, checked baggage, large quantities of carry-on baggage (estimated 25 lbs./person), up to 290 passengers and 10 members on the flight crew (estimated 180 lbs./person). The weight of the carry-on baggage, passengers and crew are estimated under existing airline policies and practices. On this DC-10, with a maximum passenger load, this estimated weight could be as much as 51.3% of this airplanes useful payload.
One might conclude that this practice of estimating the airplane weight is completely acceptable, until you consider the 78 lives lost on the Air Florida flight #90, which crashed Jan. 13, 1982 attempting to take-off from Washington National Airport in Washington, D.C. It was subsequently determined by the National Safety and Transportation Board, that the crash was due to the airplane being overweight; overweight due to snow and ice accumulations on the exterior of the airplane. Utilizing the weight and center of gravity system of the present invention which indicates the actual airplane weight and changes of center of gravity, whether forward or aft, could have alerted the pilots that their airplane was loaded beyond its certified limits and could have possibly saved lives.
When airplanes, such as the Continental Airlines flight #1713, which crashed Nov. 15, 1987 attempting take-off from the Denver Stapleton Airport, are servicing an airport with a high level of snowfall they are regularly delayed and can accumulate additional weight from snow and ice deposit on their wings and fuselages. A minor increase shown on the gross weight indicator of the present invention could alert the pilots that ice and snow deposits are accumulating, which can dislodge during flight and strike the aft engines, causing damage or even failure; justifying a pre-take-off trip back to the gate for deicing.
Fuel costs are a major concern to the airline industry. Frequently airplanes are held at the gate prior to departure, waiting for estimated weight and center of gravity calculations to be determined and transmitted from the ground computers to the pilots. Often those figures are delayed or if they come back beyond the airplanes limits, adjustments must be made at the gate. This new system progressively calculates those figures as the airplane is being loaded, giving those total figures to the pilots as the airplane doors are being closed. This being a real time measurement would allow the airplane to immediately leave the gate, thus saving fuel industry wide.
This invention relates to improvements to the previous so-called "Weight and Center of Gravity Indicators". The previous systems, use transducers of the strain gauge variety utilizing simple analog signals to transmit pressure readings for their calculations. The lack of those systems being utilized by the major air carriers, reinforces the position that those systems are not accurate nor reliable on today's more modern aircraft landing gear.
Today's aircraft landing gear struts incorporate the shock absorbing technique of forcing hydraulic fluid through a small orifice hole within the strut cylinder. Compressed nitrogen gas is used to retard foaming of the hydraulic fluid as it passes through this orifice. Changes in temperature effect the compressed nitrogen gas; as temperature increases within the strut the nitrogen gas increases in pressure, unless the landing gear strut extends to allow the increased pressure to dissipate. Multiple O-ring seals around the piston are used to retain the hydraulic fluid and compressed nitrogen gas contained within each strut cylinder. The retention of the compressed nitrogen gas and hydraulic fluid by the O-ring seals is due to the extreme amount of friction these seals maintain as they move up and down the interior strut cylinder walls. This friction causes substantial drag to this up and down movement. While this may improve the shock absorbing quality of the strut, IT DISTORTS INTERNAL PRESSURES WITHIN THE LANDING GEAR STRUT AS THOSE PRESSURES RELATE TO THE AMOUNT OF WEIGHT THE STRUT IS SUPPORTING. Temperature and hysteresis compensation factors are needed to correct for the false pressure readings caused by drag within the landing gear struts. The extreme accuracy of this new invention can be illustrated by the following example:
A McDonald Douglas DC-10 Series 30 Airplane has a maximum gross weight of 560,000 lbs. The port main landing gear strut supports a maximum of 252,000 lbs. with an internal strut pressure of 2300 psi. Proportionally each psi corresponds to 109.57 lbs. of weight supported. Utilizing Paroscientific, Inc. "Digiquartz.RTM. Intelligent Transmitter" Series 1000 Model 1003K, with an accuracy to 0.3 psi, along with temperature and hysteresis adjustments, will allow calculations of the weight in increments as close as 32.87 lbs., to this strut supporting 45% of aircraft weight, with total gross weight to be calculated to increments as close as 73.04 lbs. on this 1/2 million pound aircraft, which provides an accurate measurement within 0.013%.
The airline industry may not wish to give up the methods for estimating weights, that they have been using for years. This new system could then complement their current practices by giving the pilots a verification, of data received from the ground computers, that one or more of the input figures to the ground computer, were not entered in error or possibly that some numbers have not been transposed. The decision whether or not to attempt a take-off, ultimately is made by the pilot in command. This new system will give more accurate information, which can be used to make that decision.
Cost effectiveness is another major concern of the airline companies; getting the most revenue from each flight that an airplane makes. With the current system of estimating weight, the airline companies must factor in margins for error in their calculations, which can result in unnecessary empty seats or less cargo transported. This new system which more accurately determines the airplane weight, could reduce those margin amounts, and allow more income producing cargo to be transported on each flight.
Still another application of this new system could be the general aviation industry (the private and corporate pilots). These pilots do not have the sophisticated weight and balance computers, used by the airline companies, at their disposal. These pilots must weigh each and every item loaded on to their airplanes, or as many pilots do, just estimate or guess at it. This new system will do for these pilots those benefits discussed for the airline pilots. Many private airplane crashes can possibly be avoided by giving the private and corporate pilots better information as to the weight and balance of their airplanes. The ultimate results can be more lives saved.